<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        *{
            margin: 0;
            padding: 0;
        }
        .fa{
            width: 800px;
            height: 500px;
            background: #337995;
            margin: 0 auto;
            position: relative;
        }
        .son{
            position: absolute;
            bottom: 0;
            left: 50%;
            margin-left: -50px;
            top: 50%;
            margin-top: -50px;
            width: 100px;
            height: 100px;
            background: #18d49f;
        }
    </style>
</head>
<body>
    <div class="fa">
        <div class="son">好大儿</div>
    </div>
</body>
</html>